For the determination of ions in solutions, use is frequently made of the potentiometric ion-selective electrode (Cammann, K., Die Arbeit mit Ionenselektiven Elektroden [Working with ion-selective electrodes], 2nd ed., Springer Verlag: Berlin, Heidelberg, N.Y., 1977). Ion-selective electrodes have widespread applications in the fields of biology, chemistry and medicine, the best known example being the pH-meter.
An ion-selective membrane is the key component of most potentiometric ion sensors. It establishes the preference with which the sensor responds to the analyte in the presence of various interfering ions from the sample. If ions can penetrate the boundary between two phases, then a electrochemical equilibrium will be reached, in which different potentials in the two phases are formed. Before ion selective electrodes are capable of making their intended measurement, they have to go through some form of conditioning. This is especially important for universal ion selective electrodes (H. Bohets Analytica chimica Acta 581(1):181-91, 2007 Jan. 2) where the selectivity determining ion-pair has to be formed in situ. The time it takes a universal sensor to become conditioned can vary from as little as a few hours to as long as a few weeks and is for example dependent on the analyte to be determined and the design of the sensor being used. For example, universal ion selective electrodes typically contain a plasticized PVC based ion-selective membrane. In said electrodes the conditioning time will be determined by the time it takes for the formation of the desired ion-pair (for example substituting K+ with the analyte ion), to take place, the consistency, i.e. electrochemical equilibrium of solute membrane interface, and the hydration of the ion-selective membrane.
For some analytes, the conditioning time may be unacceptably long, and although conditioning the electrodes at a higher temperature tends to accelerate the conditioning process, the latter is not always workable, such as for example when analyzing temperature sensitive components.
Another method to increase the conditioning speed is to work at higher concentration. It has been observed that this method is often limited by analyte solubility and post conditioning relaxation (drift not obtaining full sensitivity).
Combining elevated and high concentration will yield improved conditionings speed due to the synergy of both methods. High temperature will increase product solubility and membrane permeability, whereas high concentration will increase the probability of ion pair formation in the membrane. However, balancing of temperature and concentration versus decomposition and postconditioning relaxing is not obvious and product dependent. There is accordingly a need for a fast and simple procedure that allows the end user to optimize the conditioning method of universal ISE's in a straightforward procedure for a random analyte.
It has thus been an object of the present invention to provide an improved conditioning method addressing the aforementioned problems in a simple and more uniform procedure.
Depending on the level of method complexity different solutions are proposed.                1) Using High temperature typically for stable products        2) Using High concentration typically for well dissolving products        3) Using High temperature and high concentration typically for stable well dissolving products.        4) Using flash heating (sort period of time the component is heated) typically for less stable components.        5) Using flash heating and high concentration.        6) Using flash heating and high concentration gradient.        7) Using flash heating gradient and high concentration.        8) Using flash heating gradient and high concentration gradient.        
Any of the above methods could be completed by a pulse of tensides present within the conditioning solution and/or relaxation of the ISE in an analyt solution (typically 100%) at measuring temperature.
This improved conditioning method is particularly useful in conditioning ISE's selective for difficult to condition, less stable and/or temperature sensitive products. By applying the conditioning solution at an elevated temperature and/or with a high concentration of the ion of interest, optionally with one or more of a gradually decreasing concentration of the ion of interest, flash heating and a pulse of tensides present within the conditioning solution, it has been observed that the conditioning procedure is less compound dependent. In other words, the more complex the conditioning procedure the more universal it gets. It is accordingly an objective of the present invention to provide a set of standardized ‘active’ conditioning procedures dependent on the characteristics of the analyte like, stability, solubility, temperature sensitivity and the like.